1. Field of the Invention
The invention relates to a laser repairing method of an electroluminescent display device having a plurality of pixels and an electroluminescent element provided in each of the pixels and formed by interposing an electroluminescent layer between an anode layer and a cathode layer.
2. Description of the Related Art
An organic electroluminescent (hereafter, referred to as EL) display device using organic EL elements is receiving an attention as a new display device substituted for a CRT or an LCD.
FIG. 5 is a cross-sectional view showing a structure of such an organic EL element. An anode layer 1 made of ITO (indium tin oxide) is formed on a transparent insulating substrate 10 such as a glass substrate, and an organic EL layer formed of a hole transport layer 2, an emissive layer 3, and an electron transport layer 4 is laminated thereon. A cathode layer 5 is formed on this organic EL layer. A potential difference is applied between the anode layer 1 and the cathode layer 5. When a drive current flows in the organic EL element, a hole injected from the anode layer 1 and an electron injected from the cathode layer 5 are recombined in the emissive layer 3, and an organic molecule forming the emissive layer 3 is excited to form an exciton. Light is emitted from the emissive layer 3 in a process of radiation of the exciton and then released outside after going through the transparent anode layer 1 to the transparent insulating substrate 10, thereby completing light-emission.
The above organic EL layer and the cathode layer 5 are formed by a vapor deposition method using a metal mask. In this vapor deposition process, a foreign substance 6 sometimes adheres to a region for the formation of the organic EL element. This generates a short circuit between the anode layer 1 and the cathode layer 5 so that a potential difference disappears between the anode layer 1 and the cathode layer 5. Then, the drive current does not flow in the organic EL element, and a so-called dark spot occurs in this pixel region.
To solve this problem, laser beams having a predetermined wavelength (for example, 1056 nm) are radiated to the foreign substance 6 to burn it out. This enables normal light-emission at a peripheral pixel region except the pixel irradiated with the laser beams.
However, when the laser beams are not properly radiated to the foreign substance 6, the cathode layer 5 is damaged by the energy of the laser beams and can be torn to form a pin hole at the organic EL element. Once the pin hole is formed, moisture enters the organic EL element therefrom to damage the element, resulting in a display defect of a dark spot.